The workplace may be responsible for around one in six cases of adult asthma among the British baby boomer generation - those born in the late 1950s - reveals research published online in the respiratory journal Thorax.
The strongest evidence seems to be for jobs involving cleaning or cleaning agents, the research suggests.
The authors base their findings on the job histories up to the age of 42 of almost 7,500 British adults born in 1958, all of whom were taking part in the National Child Development Study, which is tracking the long term health of more than 11,000 people living in Britain.
Information about symptoms of asthma or wheezy bronchitis was collected at the ages of 7, 11, 16, 33 and 42 from 9,500 participants.
After excluding 2,000 who had these symptoms before the age of 16, the remainder were tested for sensitivity to allergens and their lung power between the ages of 42 to 45. Participants were also asked about their work history at the ages of 33 and 42.
Their exposure to compounds known to be associated with asthma was calculated using the Asthma Specific Job Exposure Matrix (ASJEM). This assigns workplace exposure to 18 different high risk antigens, environments, and respiratory irritants.
One in four were smokers by the age of 42, when the cumulative prevalence of asthma that had started in adulthood was 9%. Most (87%) were in employment at age 42, and over half (55%) had office jobs.
Around one in four participants had only ever worked in a job that was zero risk, according the ASJEM. Just under one in 10 (8%) had ever been exposed to high risk agents; while a further 28% had ever been exposed to low risk agents. Around one in three (34%) had ever been exposed to both.
There are many occupations that are thought to cause asthma, say the authors. And in this study the start of asthma in adulthood was clearly linked to 18 types of job, including farming, which more than quadrupled the risk, hairdressing, which almost doubled the risk, and printing, which tripled the risk.
Four of these 18 jobs were cleaning jobs, and a further three were likely to involve exposure to cleaning agents.
After taking account of factors likely to influence the results, people exposed to low risk agents were 20% more likely to have asthma diagnosed as an adult than those who had not been exposed to any risk.
Those exposed only to high risk agents were 53% more likely to have the condition, while those exposed to both types of agents were 34% more likely to do so.
The high risk agents implicated were flour, enzymes, cleaning/disinfectant products, metal and metal fumes, and textile production.
All in all, the authors calculated that 16% of adult onset asthma among those born in the late 1950s could be explained by the types of jobs held.
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